Improving the Surface Oxygen Vacancy Concentration of Bi2O4 through the Pretreatment of the NaBiO3·2H2O Precursor as a High-Performance Visible Light Photocatalyst

The oxygen-deficient bismuth oxide, Bi 2 O 4, synthesized by a typical hydrothermal method using commercial NaBiO 3 ·2H 2 O as a raw material only has a relatively low concentration of surface oxygen vacancies (OVs). How to improve the visible light photocatalytic performance of Bi 2 O 4 via tuning its surface OV concentration is still a huge challenge. In this study, improving the surface OVs of Bi 2 O 4 was successfully realized through the pretreatment of commercial NaBiO 3 ·2H 2 O, including thermal treatment in air and hydrothermal treatment in 10 M NaOH solution, forming NaBiO 3 · x H 2 O intermediate products first, and then hydrothermal preparation of Bi 2 O 4 target products using NaBiO 3 · x H 2 O instead of commercial NaBiO 3 ·2H 2 O as the precursor. The enhanced surface OV content not only narrows the band gap of Bi 2 O 4 and thus extends its optical response range but also captures more photoexcited electrons and thus increases the charge carriers’ separation efficiency and prolongs the charge carriers’ lifetime of Bi 2 O 4 . Among the above-mentioned two pretreatment methods, the effects of the hydrothermal pretreatment are superior to those of the thermal treatment, involving the increase of surface OVs, the optical harvesting capacity, and the charge carriers’ separation efficiency. Accordingly, Bi 2 O 4 prepared by the hydrothermal pretreatment route exhibits the optimal visible light catalytic performance toward the removal of methyl orange (MO) and phenol due to its most abundant surface OV concentration, which is 2.59 times and 4.26 times higher than that of Bi 2 O 4 synthesized directly by the commercial NaBiO 3 ·2H 2 O route, respectively. Holes (h + ) and superoxide radicals ( • O 2 – ) are identified as the main active species, while singlet oxygen ( 1 O 2 ) and hydroxyl radicals ( • OH) are verified as the second and third important active species for organic pollutant removal, respectively. This work has developed a novel strategy to promote the catalytic performance of single Bi 2 O 4 induced by the enhanced surface OV concentration through the pretreatment of the precursor, commercial NaBiO 3 ·2H 2 O.